India enters supercritical power plant technology Variable speed drive technology: Guarantor for economic and efficient boiler feed pump drive operation Alexander Schust, Area Manager, Voith Turbo GmbH & Co. KG, Germany Wolfgang Sautter, General Manager Sales, Voith Turbo GmbH & Co. KG, Germany Presented at Power Gen India & Central Asia, New Delhi 2008 1. Status quo on power station unit sizes and boiler feed pump drive configurations within India Power station unit size [MW] Drive configuration on boiler feed pumps within Indian power market 135 2 x 100% electric motor driven boiler feed pumps with geared variable speed couplings 210 3 x 50% electric motor driven boiler feed pumps with geared variable speed couplings 250 3 x 50% electric motor driven boiler feed pumps with geared variable speed couplings 300 3 x 50% electric motor driven boiler feed pumps with geared variable speed couplings 500 2 x 50% steam turbine driven boiler feed pumps 1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit 600 2 x 50% steam turbine driven boiler feed pumps 1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit 660 2 x 50% steam turbine driven boiler feed pumps 1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit 800* 2 x 50% electric motor driven boiler feed pumps with geared variable speed couplings Figure 1: Configurations on boiler feed pump drives depending on unit sizes within India * Future concept; not yet executed within India With the first steps into supercritical power plant technology India is entering a new era in unit sizes for power stations from 600 to 1,000 MW. When having a first look into existing Indian power stations it is possible to basically divide up the Indian power market by unit sizes and further down on the boiler feed pump drive configurations as shown within figure 1 above. 2 State of the art within India is the use of steam turbines on boiler feed pump drives for unit sizes of 500 and 600 MW. The traditional concept to be followed within this power stations is 2 x 50% steam turbine driven boiler feed pumps with 1 x 50% electric motor driven boiler feed pump operated by a geared variable speed coupling as a startup and stand-by unit. For plants smaller than 500 MW, steam turbine drives are not seen anymore due to high capital cost and high efforts on maintenance to be taken. Thus, only electric motor drives are to be used either with 2 x 100% or 3 x 50% boiler feed pump drive configurations depending on specific unit sizes. All over the world, the trend goes towards unit sizes bigger than 500 MW. Correspondingly, also within India a drift to higher plant output is currently under planning and execution. Barh and Sipat supercritical projects of 3 x 660 MW each under NTPC are in an advanced stage of execution. Ultra mega power projects (UMPPs) of 4,000 MW total output are progressing fast towards realisation. The first one is Mundra with a plant output of 5 x 800 MW for Tata Power Company Limited which is currently in the execution phase. Sasan and Krishnapatnam are the next projects in line already secured by Reliance Energy Limited. With this background it is worth to take a brief general look into currently ongoing power station projects throughout the world which will form part of the following paper section. 2. New ongoing power projects worldwide Power station name Datteln 4 Staudinger Scholven Massflakte NL Neurath Hamm Ensdorf Enshafen NL Unit size [MW] 1,000 1,100 1,100 1,100 1,100 800 800 800 Boiler feed pump drives configuration 1 x 100% steam turbine driven boiler feed pump 2 x 50% electric motor driven boiler feed pump with geared variable speed coupling or 2 x 40% as start-up and stand-by unit Walsum 790 2 x 50% electric motor driven boiler feed pump with geared variable speed couplings Karlsruhe RDK 8 920 2 x 50% electric motor driven boiler feed pump with variable speed planetary gear sets Moorburg 800 2 x 50% electric motor driven boiler feed pump with variable frequency drive Figure 2: Selection on new power station projects and boiler feed pump drive configurations in Europe Within Europe current power station projects with a power range exceeding 600 MW can be divided up into power stations following the traditional concept of running a 1 x 100% steam turbine driven boiler feed pump in combination with 2 x 40% or 50% electric motor driven boiler feed pumps with geared variable speed couplings as start-up and stand-by units and several power station projects following new concepts of running the main boiler feed pumps purely on an electric basis without the use of a steam turbine on the main boiler feed pump drives. The concept to be followed will be 2 x 50% or 3 x 50% electric motor drives. In these electric motor driven configurations either geared variable speed couplings, variable speed planetary gears or sometimes variable frequency drives are being used. The table above gives a selection of several European power station projects showing the basic concepts to be followed on these power stations. 3 Power station name Unit size [MW] Boiler feed pump configuration Rodemacher Spruce 600 750 1 x 100% steam turbine driven boiler feed pump 1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit Iatan Trimble County 850 735 2 x 50% steam turbine driven boiler feed pumps 1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit Nebraska City 2 Plum Point 600 665 2 x 50% electric motor driven boiler feed pump with geared variable speed couplings Longview Dominion City 600 585 3 x 50% electric motor driven boiler feed pump with geared variable speed couplings Weston 500 3 x 50% electric motor driven boiler feed pump with variable speed planetary gear sets Figure 3: Selection on new power station projects and boiler feed pump drive configurations in the USA Within the US market, the traditional concept mainly followed in the past was a 1 x 100% steam turbine driven boiler feed pump and for start-up and stand-by purposes a 1 x 2550% electric motor driven boiler feed pump arranged with a geared variable speed coupling. Also today with new power station projects of more than 500 MW unit size, this concept is still to be seen but also Power station name Unit size [MW] within the US market a trend towards the use of electric motor drives only as main boiler feed pump drives is noticeable as per table shown above. Looking into the Chinese power market the traditional concept followed for several 600 MW units is 2 x 50% steam turbine driven boiler feed pump drives with 1 x 30% electric motor driven boiler feed pumps operated with a geared variable speed coupling as a start-up and stand-by unit. However, new power station projects within China are also leaning more and more to electric motor drives only without steam turbines as per the following table. Boiler feed pump configuration Zhaoguang Ningxia Yuncheng Minquan 600 600 600 600 2 x 50% steam turbine driven boiler feed pump 1 x 30% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit Hancheng Fenhzhen Hequ DaLaTe 600 600 600 600 2 x 50% electric motor driven boiler feed pumps with geared variable speed coupling 1 x 50% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit Pucheng 600 2 x 50% electric motor driven boiler feed pump with variable speed planetary gear sets 1 x 30% electric motor driven boiler feed pump with geared variable speed coupling as start-up and stand-by unit Figure 4: Selection on new power station projects and boiler feed pump drive configurations in China 4 3. Resulting effects on Indian power station projects Figure 5: Specification text for boiler feed pump package for 5 x 800 MW UMPP Mundra, India The trend towards the utilisation of pure electric motor drives only already influences ongoing Indian power station projects. In 2007, Tata Consulting Engineers specified electric motor drives only without any start-up and stand-by units for 5 x 800 MW UMPP Mundra. The paragraphs of the specification shown above give the wording used to specify this concept in order to put India also in line with the worldwide ongoing trend. Besides the first big step in entering into new supercritical power plant technology within India additionally another big step forward is taken at the same time when specifying and executing drive packages as per package No. 1 above without the use of a steam turbine on the main boiler feed pumps and without the use of any start-up and stand-by units. These huge steps taken into further development of Indian power Figure 6: Specification text for boiler feed pump drives for 5 x 800 MW UMPP Mundra, India plant technology will influence further upcoming projects within India and will set new standards within power station unit sizes, drive technologies in terms of plant efficiency, cost impacts and reliability issues. By going to a 2 x 50% boiler feed pump arrangement without stand-by unit, the reliability of the boiler feed pump trains is of utmost importance. Thus, reliability of each component of the drive train has to be evaluated with a special focus on the variable speed drive system itself. Therefore most power plants around the world using this 2 x 50% configuration have decided to use hydrodynamic variable speed drives due to its superior reliability. The key factor is to be really seen as highest required reliability on the drive systems used on the boiler feed pump drives in order to not affect the plant output. As a result of this insight Tata Consulting Engineers specified hydrodynamic drives on the boiler feed pumps. This is shown within the following specification text where Tata Consulting Engineers specified geared variable speed couplings only. Also it can be noted that Tata Consulting Engineers specified the first time ever within India the highly efficient variable speed planetary gear drive as an option to the conventional geared variable speed couplings also shown in the specification text above. With this common trend towards electric motor drives all over the world it is now worth to take a closer look into the different boiler feed pump configurations with electric motors only. This will form part of the next paper section. 5 4. Boiler feed pump drive configurations for electric motor drives Option (A) 3 x 50% GVSC Option (B) 2 x 50% GVSC Figure 7: Electric motor drive configurations on boiler feed pumps GVSC Geared Variable Speed Turbo Coupling VSPG Variable Speed Planetary Gear Set For electric motor drives on boiler feed pumps it can be distinguished between drive configurations as per chart given above within figure 7. 6 Option (A) is reflecting the traditional concept with a configuration where 2 x electric motors run 2 x main boiler feed pumps supplying feed water into the boiler. Both boiler feed pumps are operated on variable speed with a geared variable speed coupling installed in the drives. Additionally, an electric motor drive facilitates the start-up procedure by filling the system with water and serves as a stand-by unit in case one of the boiler feed pumps trips. This stand-by unit is also operated as a variable speed pump via a geared variable speed coupling. Having the additional stand-by unit provided, this drive configuration displays together with option (C) the most safe way to operate the plant and in addition to that, in any case a more economic way as by utilising a steam turbine in the drive. Option (B) is probably the most modern and as a matter of fact, most economic drive configuration. Especially for tariff based bidding processes, this is the most attractive solution. This system is introduced within India on 5 x 800 MW UMPP Mundra where 2 x 50% main boiler feed pumps are proposed to be driven via geared variable speed couplings by electric motors only. For this specific drive configuration no stand-by unit is specified leading to the necessity that the installed drives are required to prove for highest reliability throughout the complete lifetime of the plant. Having no steam turbine and additionally saving the money in cutting down the investment for a separate stand-by unit, this drive configuration reflects by far the most economic drive system in power utilisation. Option (C) 2 x 50% VSPG + 1 x 30% GVSC Option (C) fitted with variable speed planetary gear sets on the main boiler feed pumps offers the highest drive efficiencies – of course on the basis of higher initial costs – also resulting in a better plant efficiency than drive configurations as per options (A) and (B). High drive efficiencies are especially inherent to the variable speed planetary gear set and are put into place most effectively when operating at variable plant loads. This advantage of high drive efficiency with the variable speed planetary gear set is especially paid off against other drive systems used. Having additionally a stand-by unit installed on the drive configuration for option (C) this option reflects a compromise between options (A) and (B) for electric motor driven boiler feed pump drives. As the stand-by unit is designed smaller than as for option (A), the investment for this unit within option (C) is more attractive than within option (A). In case of a failure of one of the main pump trains almost full plant load can be achieved with the stand-by unit. The additional investment on the variable speed planetary gear sets within option (C) over option (A) with geared variable speed couplings installed on the main boiler feed pump drives will certainly pay back due to high efficiency of the drive systems inherent to it. Thus, option (C) displays an agreement in both, satisfying a safety-oriented plant philosophy in having a separate stand-by unit, as well as economically offering the most competitive solution with regard to drive systems with steam turbines or traditional 3 x 50% electric motor driven units installed on the drive systems. As all these drive configurations are based on hydrodynamic variable speed drives it is now time to look into this specific technology more closer. 7 5. Facts about hydrodynamic turbo couplings and variable speed drive systems 1 2 3 1 2 3 6 8 5 Figure 8: Foettinger Principle as a basis for hydrodynamic turbo couplings Figure 9: Sectional view of a hydrodynamic variable speed turbo coupling 1 Impeller (primary wheel) 2 Circulating operating fluid 3 Turbine wheel (secondary wheel) 1 2 3 4 5 6 7 8 Hydrodynamic turbo couplings are based on the Foettinger Principle where the input power developed by a prime mover is converted from mechanical energy acting on the impeller (primary wheel) into kinetic energy within the operating fluid and converted back into mechanical energy at the turbine wheel (secondary wheel) connected to the driven machine. 8 Impeller (primary wheel) Turbine wheel (secondary wheel) Shell Scoop tube housing Oil tank Oil circulation pump Scoop tube Oil cooler To get variable speed on the driven machine, the oil filling of the hydrodynamic turbo coupling has to be regulated. An additional component, a so-called scoop tube, installed into the hydrodynamic turbo coupling allows the adjustment of the working oil filling inside the coupling while in operation. This reflects a hydrodynamic variable speed turbo coupling. 4 7 1 9 Variable speed offers … 6 11 10 7 reduced energy consumption = energy and cost savings process adaptation = reduced emissions and less pollution load pattern orientation = increased flexibility by orientation on actual plant output speed adaptation = increased service life of installed equipment and in addition hydrodynamic variable speed drives offer … 12 simple robust mechanical design = reduced maintenance requirements 5 2 8 3 4 Figure 10: Sectional view of a hydrodynamic variable speed coupling with integrated gear stage 1 2 3 4 5 6 7 8 9 10 11 12 highest availability and reliability = process stability compact design = less space needed, less investment costs load free motor start-up = start-up possible under bad power grid conditions vibration dampening features = shocks from motor or driven machine are not transmitted integrated lube oil system = no additional separate lube oil system needed Figure 11: Benefits of variable speed and hydrodynamic variable speed drives Gear stage Hydrodynamic variable speed turbo coupling Scoop tube Electro-hydraulic positioning control (VEHS) Working oil cooler Lube oil cooler Main lube oil pump Oil circulation control valve Working oil pump Auxiliary lube oil pump Reversible duplex filter Oil reservoir For typical boiler feed pump drives running at high output speeds of approximately 5,000 rpm to 6,000 rpm hydrodynamic variable speed turbo couplings can be combined with one or more gear stages in a common housing. As all these drives act on the same basic operational principle they all imply the same advantages belonging to hydrodynamic power transmission technology. In addition all benefits common to variable speed drive systems are also realised when installing these drives. An overview on these benefits is given within figure 11 above. 9 D A B C Pu ⬃ 25% Pe Figure 12: Sectional view of a hydrodynamic variable speed planetary gear set and principle of power splitting Variable speed planetary gear set A Hydrodynamic torque converter B Stationary planetary gear C Revolving planetary gear D Oil supply system Due to physical laws, efficiency of the drives as described before decreases as the output speed of the drive systems goes down. To come around this, the variable speed planetary gear set used within drive configuration (C) of section 4.) of this paper introduces the principle of power splitting into variable speed drives technology. Within its 10 Variable speed planetary gear set Principle of power splitting Pe Input power Pu Superimposing output Pa Output power components the variable speed planetary gear set consists of one or more hydrodynamic circuits in combination with mechanical gears as per each individual application required. Figure 12 illustrates the setup of the individual components of the hydrodynamic variable speed planetary gear set and the principle of power splitting applying to it. ⬃ 75% Pa 100 A Efficiency [%] 80 B 60 40 0 0 20 40 60 80 100 Load [%] Figure 13: Efficiency curves of hydrodynamic variable speed drives A Variable speed planetary gear set B Geared variable speed coupling Within this power splitting principle, the majority of power is transmitted mechanically, directly via the main shaft and the rotating planetary gear. Only that portion of input power necessary for speed adjustment of the driven machine is split from the main shaft via the adjustable hydrodynamic torque converter and superimposed on the rotating planetary gear set. Due to the high portion of mechanically transmitted power, the entire unit has an efficiency of over 95% over a wide operating range as shown in figure 13 of this paper. 11 C Ne Ne Nu Nu Na Na Figure 14: Output speed variation with a variable speed planetary gear set Variable speed planetary gear set C Revolving planetary gear Within the hydrodynamic variable speed planetary gear set the output speed is controlled by adjusting the superimposed speed. The maximum superimposed speed results in the highest output speed. A reduction or reversal of the superimposed speed results in a reduced output speed. This is shown within figure 14 above. Ne Input speed Nu Superimposed speed Na Output speed Ring gear Planet Planet carrier Sun gear 3-D-view of revolving planetary gear 12 Vorecon type RW boiler feed pump, Germany Power 8,500 kW Speed 5,000 rpm A 1 2 3 Figure 15: Set-up of a hydrodynamic torque converter as part of the variable speed planetary gear set Variable speed planetary gear set A Hydrodynamic torque converter The superimposed speed itself is varied by adapting the oil flow inside the hydrodynamic torque converter by operating and adjusting internal guide vanes. Figure 15 above shows the location of the hydrodynamic torque converter (A) inside the variable speed planetary gear set as well as its setup. Hydrodynamic torque converter 1 Adjustable guide vanes 2 Pump wheel 3 Turbine wheel As now the technique applying to hydrodynamic variable speed drives is systematically illustrated, the upcoming paper section focuses especially on the commercial assessment of these drives. 13 6. Commercial evaluation on different variable speed drive systems VSPG ⬃ 45 m2 Motor VSPG Motor Gear Cooling system VFD ⬃ 150 m2 Harmonic filter Isolation transformer Oil system Cooling system Frequency drive Figure 16: Comparison in field conditions of different variable speed drive systems VSPG Variable speed planetary gear VFD Variable frequency drive To find the most economical drive system, a thorough analysis of lifecycle cost has to be done. This analysis should include equipment cost, installation and infrastructure cost, commissioning and maintenance cost as well as energy cost. 14 The variable speed planetary gear drive system is very simple and requires few components, compared to a variable frequency drive system as shown within figure 16 above. This results in less required space, less cost for setting up buildings and more simple installation and commissioning. Equipment cost are significantly lower, especially for high power applications. Due to the high reliability of the variable speed planetary gear drive system, maintenance and repair cost are extremely low. Overhead tank 13.8 kV Motor losses VSPG losses Motor VSPG Working machine Power for cooler (fans) Transformer VFD losses losses Motor losses Gear losses Motor Gear Working machine VFD 13.8 kV Optional input filter losses Filter losses Power for cooling system Power for air conditioning Power for cooler (fans) Power for oil system (pumps) Figure 17: Systemic efficiency line-up of different variable speed drive systems VSPG Variable speed planetary gear VFD Variable frequency drive Furthermore, energy cost for the variable speed planetary gear set is similar to a variable frequency drive when a sound evaluation in comparing the entire drive system is done. For this purpose it has to be ensured that all relevant component efficiencies are included in the considerations. Figure 17 illustrates that with a variable frequency drive system a lot more drive components are set in place reducing drive efficiency than as for the variable speed planetary gear set. All these different additional drive components imply additional power losses with the result of more energy consumed for the variable frequency drive system. 15 Load pattern (4 x 800 MW) Operating points Summer 75% 100% MCR 100% BMCR 103% BMCR 103% Design Point Point A Point B Point C Point D Point E Point F 500 500 7,000 10 10 5 Power consumption of pump (kW) 4,463 6,652 11,164 11,842 12,963 13,382 Operating speed (rpm) 3,663 4,131 4,804 4,890 5,008 5,069 Motor efficiency 97.0% 97.3% 97.7% 97.7% 97.7% 97.7% VFD efficiency 96.5% 97.0% 97.5% 97.5% 97.5% 97.5% Transformer efficiency 99.0% 99.0% 99.0% 99.0% 99.0% 99.0% Isolation transformer efficiency 99.0% 99.0% 99.0% 99.0% 99.0% 99.0% Gear box efficiency 98.0% 98.2% 98.5% 98.5% 98.5% 98.5% Overall efficiency 89.9% 90.8% 92.0% 92.0% 92.0% 92.0% Operating time (hours per year) Drive system efficiency & electrical power consumption VFD Electrical power consumption (kWh/a) VSPG 2,481,998 3,661,473 84,979,089 128,771 140,961 72,759 Lube oil pump (30 kW estimated) 15,000 15,000 210,000 300 300 150 Motor efficiency 97.2% 97.5% 97.9% 97.9% 97.9% 97.9% Vorecon efficiency 86.2% 87.8% 94.8% 95.1% 95.1% 94.9% Transformer efficiency 99.0% 99.0% 99.0% 99.0% 99.0% 99.0% Overall efficiency 82.9% 84.7% 91.9% 92.2% 92.2% 92.0% 2,690,222 3,924,532 85,053,393 128,477 140,639 72,746 193,225 248,060 -135,695 -594 -622 -163 0.03 0.03 0.03 0.03 0.03 0.03 Savings per year in Euro 5,797 7,442 -4,071 -18 -19 -5 Total savings (S) with VFD per year 9.126 Euro Electrical power consumption (kWh/a) Energy savings with VFD system Power savings with VFD system (kWh/a) Power cost (Euro/kWh) Investment VFD VSPG Payback calculation Estimated VFD system cost Price VSPG VFD 1,600,000 Euro Gear 150,000 Euro Oil supply system 90,000 Euro Extra price motor 50,000 Euro Wiring 80,000 Euro Total 1,970,000 Euro VSPG 950,000 Euro Difference in cost (C) Euro 1,020,000 Interest rate (i) % 8% Cost increase (f) %/a Payback formular 3% N = log (r/(r-i)/log (1+i) Payback rate Payback rate r = (S-C*f)/C Payback time -21 years, 7 months Figure 18: Example of a payback calculation for different variable speed drive systems VSPG Variable speed planetary gear VFD Variable frequency drive 16 -0.021052647 Best to illustrate economic advantages of hydrodynamic variable speed drive systems over variable frequency drive systems is to perform an objective payback calculation evaluating the different drive efficiencies as well as the difference in investment cost for the evaluated drive systems. Figure 18 shows this exemplarily for a power station convoy of 4 x 800 MW. The load pattern of the power plant is the basis for the evaluation and is used to calculate the electrical power consumption in kWh/a for the different drive systems looked into. On doing so, it is absolutely essential to evaluate the different drive systems on the basis of all components installed as pointed out above. It has to be a systemic view, each drive system has to be evaluated in total, not just in its single components only. For the evaluation done within figure 18, energy cost for the variable frequency drive system are less than for the variable speed planetary gear set due to having slightly better overall efficiency values for the given load pattern. This leads to total energy savings of Euros 9,126.00 per year when operating the variable frequency drive system. To complete the economic evaluation, the investment side has to be considered resulting in a payback calculation to be performed. Based on a certain interest rate and cost increase per year, a net present value calculation incorporates the total energy savings calculated in combination with the difference in investment cost between the different variable speed drive systems. With the variable speed planetary gear drive, the initial cost are much lower than with the variable frequency drive system with its advantages in cost savings on the energy side. Thus, even with money being saved on the energy side, the variable frequency drive system will not pay back due to having a negative payback calculated. The higher investment cost of the variable frequency drive system cannot be recovered, not even in a 20 or more years plant life. The outcome of this payback calculation shows the advantages of the hydrodynamic variable speed drive in being the most competitive drive system. In combination with drive configuration (B) or (C) of section 4 of this paper, tariff-based project bids can be viewed as best served when installing hydrodynamic variable speed drive systems due to being able to offer real economic advantages to utility companies and power station owners. 17 7. Conclusion Reliability figures of hydrodynamic variable speed drives (based on data available on variable speed planetary gear drives) No. of units evaluated 69 Power range [kW] 600 - 11,931 Output speed [rpm] 495 - 16,482 Total operating hours 2,095,921 No. of reported failures 6 Non availability time [hrs] 546 Reliability calculation: (2,095,921 - 546) / 2,095,921 = 99.97 % (based on machines in operation) MTBF calculation: 2,095,921 / 6 = ~ 39 years (based on machines in operation) Figure 19: Reliability figures of hydrodynamic variable speed drives (variable speed planetary gear drives) On the background of the ongoing trend towards higher plant output combined with tariff-based project bidding systems the ambition towards a most economic operation of a power plant plays a vital role for successfully running a state of the art power station. Within this, hydrodynamic variable speed drives are able to offer all its inherent success factors to utility companies and power station owners. Objective payback calculations give proof of that. 18 Operating a hydrodynamic variable speed drive system realises all advantages which belong to variable speed drives in general in combination with all success factors essential to hydrodynamics as the operational principle of the drive systems. In this respect, more flexibility offered by the use of the hydrodynamic variable speed drive system means highly efficient and environmental-friendly processes can be realised while saving money at the same time. Thus, efficiency of the drive systems used has to be seen as yet another success factor a drive system should be evaluated on. Objective efficiency comparisons performed on a systemic view are able to give evidence of this. Durability of the drive system installed has to be seen as a further success factor of essential interest to the utility companies aspiring a most satisfactorily operating plant. A drive system shall be designed for a minimum of the life time of the whole plant, thus, a minimum of at least 25 years of operation should be considered as basis for a drive evaluation. This means a minimum of at least 25 years of operation where spare parts availability has to be ensured. The technology used has to be long-lasting, not rapidly changing. Proven mechanical components still being available within 30 years from today form the basis of a trustworthy alliance to a hydrodynamic variable speed drive system on which this can easily be proven for. = Efficiency VFD versus VSPG Economics Reliability Durability Figure 20: Success factors for evaluation of variable speed drive systems VSPG Variable speed planetary gear VFD Variable frequency drive Highest reliability of the drive system acts as the basis for longest operating hours to be realised for economic plant operation. Downtime of the plant is most cost-intensive and has to be avoided in order to ensure smooth production. Availability is the most critical factor when calculating the life-cycle cost of an installation. Using a hydrodynamic variable speed drive system proves for a reliability of 99.97% or in other words, an MTBF of more than 39 years based on machines in operation as shown within figure 19 can be adhered to. In pursuing the optimum solution for each individual power station project, it becomes clear that an objective assessment of different drive systems has to be done on the basis of 4 essential success factors as shown in figure 20 above. 䡲 Drive reliability counts as nothing can compensate for lost production. 䡲 Drive economics count as only the most economic system will sustain thorough payback evaluations done. 䡲 Drive durability counts as only a constant running system proves for the economic figures being expected. 䡲 Drive efficiency counts as only adapted processes to be run help saving money. On this background it becomes clear that all four success factors have to interlock into each other in order to develop an overall drive system evaluation showing the optimum solution to the decisionmakers. Considering a hydrodynamic variable speed drive system within such an evaluation will, in all respects, surely pay back. 19 Voith Turbo Private Limited P.O. Industrial Estate Nacharam Hyderabad – 500 076 Tel: +91 40-27 17 35 61, 27 17 14 40 Fax: +91 40-27 17 11 41, 27 17 31 34 info.hyd@voith.com www.voithturbo.com Cr 605 en, 04.2009, aik / SVG, 600. Printed in Germany. Subject to modification due to technical development. Voith Turbo GmbH & Co. KG Variable Speed Drives Voithstr. 1 74564 Crailsheim, Germany Tel: +49 7951 32-261 Fax: +49 7951 32-650 vs.drives@voith.com www.voithturbo.com/variable-speed